Strength and fracture toughness of the ESIS silicon nitride reference material

The ESIS Technical Committee for Ceramics (TC6) is running a joint program to characterise a commercial silicon nitride ceramic with respect to all properties necessary to a proper design process. In this paper some preliminarily results of measurements on the ESIS Reference Silicon Nitride are presented: the room temperature 4-pt. bending strength is around 870 MPa and the 3-pt. bending strength is around 990 MPa. These two data clearly demonstrate the volume dependence of strength, which can consistently be described with the Weibull theory and a Weibull modulus of about 15. The room temperature fracture toughness of the material is 4,9 MPam1/2 (determined with the SENB V method). IF-toughness values are between 4,8 to 7,9 MPam1/2. Although some sub-critical crack growth exists at room temperature (the crack growth exponent is around 50), severe time dependent damage starts around 1000°C.